Skid control system components

ABSTRACT

Deceleration controlled skid control automotive braking system components including a controller, a power booster and a variable proportioning device are disclosed. The controller utilizes the force produced upon accelerating (or decelerating) a mass suspended in low friction bearings within a housing, to actuate a three-way valve having high and low supply pressures imposed across it. The three-way valve is constructed to provide a control fluid pressure which varies as a function of vehicle deceleration, and is adapted to serve as the supply pressure for power actuated devices, such as the power booster and the variable proportioning device. The controller includes a device modifying the action of the three-way valve upon sudden reduction in vehicle deceleration, to change the control fluid pressure and modify the action of the power booster upon such sudden reduction in deceleration indicating impending wheel lock-up, for skid control. The power booster and variable proportioning device are constructed to utilize the varying control pressure produced by the deceleration actuated three-way valve as the air supply pressure.

United States Patent [191 Rockwell [11] 3,829,171 [451 Aug. 13, 1974 SKID CONTROL SYSTEM COMPONENTS Inventor: Edward A. Rockwell, 167 Ashdale Pl., Los Angeles, Calif. 90049 Filed: Aug. 3, 1971 Appl. No.: 168,683

[52] US. Cl. 303/24 C, 303/6 C Int. Cl B60t 8/18 Field of Search 303/6 C, 10, 24 A, 24 C,

5/1965 Hager 303/24 R X 11/1969 Bratten et a1. 303/24 C Primary Examiner-Duane A. Reger Attorney, Agent, or Firm-Wolfe, Hubbard, Leydig, Voit & Osann, Ltd.

[ 5 7 ABSTRACT Deceleration controlled skid control automotive braking system components including a controller, a power booster and a variable proportioning device are disclosed. The controller utilizes the force produced upon accelerating (or decelerating) a mass suspended in low friction bearings within a housing, to actuate a three-way valve having high and low supply pressures imposed across it. The three-way valve is constructed to provide a control fluid pressure which varies as a function of vehicle deceleration, and is adapted to serve as the supply pressure for power actuated devices, such as the power booster and the variable proportioning device. The controller includes a device modifying the action of the three-way valve upon sudden reduction in vehicle deceleration, to change the control fluid pressure and modify the action of the power booster upon such sudden reduction in deceleration indicating impending wheel lock-up, for skid control. The power booster and variable proportioning device are constructed to utilize the varying control pressure produced by the deceleration actuated threeway valve as the air supply pressure.

11 Claims, 21 Drawing Figures a t 1 A//9-.\

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sum 8 BF 9 b a w (M m W 7 1 SKID CONTROL SYSTEM COMPONENTS BACKGROUND OF THE INVENTION This application is related to copending applications of Harvison C. Holland, Ser. No. 708,880, filed Feb.

28, 1968, entitled Method for Producing Maximum Vehicle Deceleration, now US. Pat. No. 3,642,328, issued Feb. 15, 1972 and Ser. No. 54, 206, filed July 13, 1970, entitled Variable Ratio Proportioning Device", and the copending application of Harvison C. Holland and Edward A. Rockwell, Ser. No. 83,732, filed Oct. 26, 1970 entitled Skid Control Brake System".

Whereas copending application Ser. No. 83,732 directed to a Skid Control Braking System is the. joint invention of Edward A. Rockwell and Harvison C. Holland, this application is directed to components and combinations of components for automobile braking skid control, and particularly, but not exclusively, components utilized in that Skid Control Braking System for sensing changes in vehicle deceleration indicating impending skidding and for operating various power actuated devices for skid control.

The present invention is, therefore, directed to improvements in vehicle power braking systems in genera], and, in particular, to deceleration responsive means for controlling various power actuated components, as well as combinations of the deceleration responsive means with components that may be used in brake systems for automotive vehicles, including skid control brake systems.

Numerous automotive skid control braking systems have been devised in the past. In one type of system, a group of speed sensors are employed to detect the skid condition at each of the wheels, or at each pair of wheels of the automobile, and to modulate the fluid pressure for that wheel or wheel pair in response thereto. In that type of system the dual master cylinder which is also conventionally utilized, provides substantially equal front and rear brake line pressures. Valves are also sometimes utilized to vary the relationship of front to rear brake line pressures, but these devices typically provide a relationship consisting of two linear segments over the range of tire-road coefficient of friction values, and have no adjustment for disposable load in the vehicle.

However, an inherent problem associated with these types of braking systems is caused by the fact the relationship of front to rear braking forces does not account for the wide variation in tire-road coefficient of friction due to different road conditions, or vehicle loading, and typically provides optimum braking effect for only one or two conditions of tire-road coefficient of friction at one particular vehicle disposable load.

For example, under icy or glazed low tire-road coefficient of friction conditions, the maximum achievable braking effect and the weight shift to the front wheels at maximum braking will be low, and the front wheels will usually start to skid before the rear wheels begin to skid and thus before the maximum stopping force is achieved even for such poor braking conditions. Under dry road high tire-road coefficient of friction conditions, on the other hand, the maximum achievable braking effect and the weight shift to the front wheels at maximum braking will be high, and the rear wheels will usually start to skid before the front wheels start to skid.

With a conventional automobile having four wheels, with brakes at front and rear, according to the concept explained in copending application of Harvison C. Holland, Ser. No. 708,880, entitled Method for Producing Maximum Vehicle Deceleration" for each distribution of disposable load there is only one optimum ratio of braking forces between front and rear for a given coefficient of friction between the tires and the road that will provide maximum deceleration. This is a fundamental relationship based upon the configuration of the vehicle and its braking system.

This relationship takes into consideration the weighttransfer effect during braking which tends to increase the downward force at the front wheels and lessen the force at the rear wheels even though the total downward force of the vehicle on the road is the same as when standing still. Since the maximum braking force obtainable from a given wheel is equal to the downward force on the road times the coefficient of friction between the tire and the road, it can be seen that the front wheels can provide a greater proportion of the total braking force, and the rear wheels a lesser proportion as the maximum adhesion obtainable between the tires and the road increases.

According to the invention described in copending application of Harvison C. Holland, Ser. No. 54,306, filed July 13, 1970 for Variable Ratio Proportioning Device, the stopping force relationship described above may be obtained with the conventional hydraulic brake system by including a proportioning device, shown as a valve connected in the brake lines. This proportioning device is supplied with high pressure fluid from the master cylinder of the brake system, and transmits fluid at regulated pressure to the rear wheel brakes. According to that invention, the fluid pressure in the brake lines to the rear brakes is varied according to a predetermined function of the brake line pressure supplied from the master cylinder, so as to vary the braking effect between front and rear wheels as vehicle deceleration changes. The device is effective to vary the ratio of the brake line pressures between the front and rear brake lines as a non-linear function of vehicle deceleration and is adjustable for disposable load to obtain the stopping force relationship derived by Harvison C. Holland and takes into account the weight and center of gravity characteristics of the vehicle, and the braking characteristics of the wheel brake mechanism with which the vehicle is equipped, in order to obtain optimum proportioning of braking force for maximum braking under all road and load conditions.

With a braking system having such a variable proportioning device but without skid detection and control, since the front and rear wheels both reach their maximum braking force at the same time, it is clear that both the front and rear wheels will begin to skid substantially simultaneously at a point when the braking force applied to the wheels as a result of increased pressures in the brake lines exceeds that required to produce the maximum stopping force achievable under the given tire-road friction conditions. It has, furthermore, been observed that the impending skid condition of the automobile caused by the start of wheel lock-up will be reflected in a sudden reduction in the rate at which the automobile decelerates.

DESCRIPTION OF THE INVENTION The present invention relates generally to control devices and, more particularly, concerns a controller consisting of a decelerometer for measuring acceleration or deceleration and for producing. a control pressure which varies as a function thereof and an augmentor for momentarily modifying, or augmenting, the control pressure upon a sudden reduction of deceleration. In a preferred, exemplary embodiment, this invention provides a decelerometer having a valve device operable to measure deceleration and produce a control pressure which varies as a linear function of deceleration and an augmentation device operable to momentarily modify the control pressure on sudden reduction of deceleration.

One of the principal objects of this invention is to provide acceleration or deceleration responsive valves which are capable of controlling sufficient flow of fluid to serve as a source of pressure fluid for operating power activated devices such as recording instruments or servo mechanisms without supplemental assistance.

' Another principal object of the invention is to providedeceleration and change of deceleration responsive pressure fluid control means which is adapted to serve as a variable pressure fluid source for use in automotive brake systems having skid control features.

More directly stated, a general object of the present invention is to provide a decelerometer which isparticularly adapted to function as a vehicle deceleration responsive control unit in an automotive-brake system embodying a skid control system of the type described in said copending application Ser. No. 83,732. That system incorporates variable proportioning to vary the ratio of the brake line pressure between the front and rear brake lines as a non-linear function of deceleration to obtain minimum stopping distances under any road condition for any disposable load, and one of the objects of this invention is to provide a controller which will detect changes of vehicle deceleration that reflect an impending skid, on various types of road surfaces and responsive to such changes of deceleration will operate a power unit embodied in the system so as to reduce the braking force on all four wheels below the level which will cause wheel lock-up, to prevent skidding. Without variable proportioning of brake line pressures between rear and front brake lines which is provided for in the system, reducing braking force to prevent skidding responsive to deceleration changes of the vehicle itself would not allow optimum braking since such changes in deceleration would occur upon skidding of either front or rear wheels, whichever occurs first, and thus prematurely stop the skid. With provision in the system for variable proportioning and adjustm ent for changes in loading between front and rear brakes, detection of the deceleration changes due to impending skidding comes at substantially the exact point when maximum stopping force has been achieved.

A more specific object is to provide inertia-mass operatedthree-way valves to serve the function of decelerometers by producing a modulated control pressure which is a'function of deceleration or acceleration. A related object is to provide such valves which are highly precise. and fast in response to changes in deceleration.

A still more specific, but important, object is to provide highly sensitive deceleration or acceleration responsive three-way valves of the self-lappin g type, actuated by an inertia-mass and so balanced by pressure responsive reaction elements to provide minimum valve travel so as to obtain maximum speed of operation. An other more specific object is to provide animproved construction for three-way valves, employing valve A further specific object is to augment the change in control pressure supplied by such valves in response to high rates of reduction of deceleration .so as to increase momentarily the magnitude of change in control pressure output during impending wheel lockup.

Another object of the present invention is to provide a separate control means associated with a decelerometer which is effective to cut-in and cut-out the action of the decelerometer, so as to confine operation to desired periods. a I

Yet a further object of the invention is to provide a decelerometer and a variable proportioning device --which function together in a brake system to vary the ratio of front to rear brake line pressures as a function of deceleration, to achieve maximum stopping force for any given tire-road condition.

A more detailed object of this last aspect of the present invention is to provide a decelerometer and a variable proportioning device which function together in a brake system to control braking forces, wherein the proportioning device being controlled responsive to deceleration is operable to vary the ratio of braking forces produced by the front and rear wheel brakes as a nonlinear function of tire-road coefficient of friction, which non-linear function substantially matches the Holland equation for Sf/Sr to match the requirements of the vehicle to produce maximum deceleration under any given tire-road condition at various vehicle loadings.

Still a more detailed object of this aspect of the present invention is to provide the combination of a decelerometer and a variable proportioning device wherein the power required to operate the variable proportioning device is supplied by the decelerometer output, such that the force or power supplied by an operator to the brake pedal is wholly available to increase the brake line pressure within the braking system.

A further object of the present invention is to have the decelerometer simultaneously control (1) the power wall assembly of the power booster in response to changes in deceleration indicating impending wheel lock-up, to momentarily reduce the braking force and then to increase the braking force and thereby modulate the brakingforce about the tire-road skid point, and, (2) the variable proportioning device to vary the ratio of braking forces produced by the front and rear brakes as a non-linear function of deceleration, which function substantially matches the Holland equation for S S t o rn at cl1 tl1e requirements of the vehicle as loaded to produce maximum braking force and hence deceleration under any given tire-road condition.v

A further object is to utilize the decelerometer output pressure for controlling the supply pressure utilized to operate the power booster and to limit the differential between the supply pressure and the power chamber pressure to a substantially constant positive value of small magnitude, so as to inhibit spiking.

Other objects will become evident from the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a schematic representation of a vehicle during deceleration;

. FIG. 2 is a graph of the ratio S,/S, plotted against and rear braking force, respectively, plotted against hydraulic system pressure;

FIG. 5 is a graph also illustrating two curves, front brake system pressure and rear brake system pressure, respectively, plottedagainst F FIG. 6 is a graph of front brake line system pressure plotted against rear brake line system pressure;

FIG. 7 is a graph illustrating design curves for the proportioning device;

FIG. 8 is a graph of coefficient of friction plotted against slip ratio; v

. FIG. 9 is a graph showing two pressure curvesplotted against deceleration, one for the controller and one for the power booster;

FIG. 10 is a schematic view of the components as they may be combined to form a skid control system;

shown in cross section in FIG. 11b in different positrons;

FIG. 15 is a fragmentary view showing a speedometer cable take-off mechanism and pressure control valve associated with the controller shown in FIG. 11b;

FIG. 16 is a graph of deceleration and supply pressure plotted against time for the controller; and

FIG. 17 is a graph of valve closing plotted against valve opening distance.

' THE SYSTEM IN GENERAL Now turning to the drawings, FIGS. l-10 are schematic illustrations and graphs to assist in the explanation which will be given of the Holland method of producing maximum vehicle deceleration, which method has been followed in the development of the compo- 6 nents of the braking system'schematically shown in FIG. 10. i

.In general, by following the Holland method, a brake system has beendeveloped which varies the proportioning of braking forces front to rear in a manner determined by the configuration of the particular vehicle on which the system is used,so as to match the requirements of that vehicle to produce maximum deceleration under any given road conditions. Since with a braking system having such variable proportioning, the front and rear wheels both reach their maximum stopping force at the same time, both the front and rear wheels will begin to skid simultaneously at a point when thebralcing force applied to the wheels through the brake system exceeds the maximum stopping force that can be developed at the road surface under the prevailing coefficient of friction conditions. It has been observed that the impending skid caused by the start of wheel lock-up when the tires break free of the road surface willbe reflected in a sudden change of the rate at which the vehicle decelerates. According to an aspect of the present invention a controller that is responsive to sudden reduction in deceleration of the vehicle is utilized to'modulate the total braking forces applied by the system about their maximum points at both front and rear wheels to maintain substantially maximum vehicle deceleration without skidding.

The hydraulic brake system shown substantially in FIG. 10 includes the conventional elements of front and rear brakes 30, 32, separate front and rear brake lines or sub-systems 34, 36 and a dual master cylinder 38 producing front and rear brake line pressures in response to application of the brake pedal 40 by the operator. I

In addition, the brake systemincludes certain ele-,

ments and combinations of elements which are constructed according to the present invention. Thus, a power booster 42 actuated by the brake pedal 40 to provide power assist to operate the dual master cylinder 38, is controlled by a controller 46 which functions independently of and in conjunction with the booster differential between the supply pressure, conveyed to the booster control valve, and the power chamber pressure, in order to inhibit spiking or extremely fast and hard braking. Second, in the condition of brake operation reflecting an impending skid, the controller momentarily reduces the supply pressure to produce a negative differential between the supply pressure and the power chamber pressure causing the power chamber pressure to dropand thereby returning the power wall and reducing the braking force on all four wheels below the level which will cause wheel lock-up, to prevent skidding. As the supply pressure increases after momentary reduction, the controller reproduces a positive differential between the supply pressure and the power chamber pressure, such that upon normal continued manual application of the brake pedal the booster power wall is reapplied to reapply the braking the method of producing maximum vehicle deceleration set forth in detail in copending application of Harvison C. Holland, Ser. No. 708,880, entitled Method for Producing Maximum Vehicle Deceleration, filed Feb. 28, 1968. A brief description of that Holland Method is included for purposes of fully explaining the present invention.

THE HOLLAND METHOD The Holland concept as set forth in said application Ser. No. 708,880 is based upon the discovery that for .any vehicle having front and rear brakes, there is one (and only one) front to rear stopping force ratiothat will produce maximum deceleration at each coefficient of friction between the tires and the road. This is a fundamental relationship and takes the form of the follow ing equation:

f/ r c c l where Y is the horizontal distance from the rear wheels to the center of gravity of the vehicle. X is the horizontal distance from the front wheels to the center of gravity, Z is the vertical distance from the road surface to the center of gravity, and S; and S, are the stopping forces at the front and rear tires respectively due to tire-road friction, and F. is the coefficient of friction between the tire and road.

Briefly detailing the concept more fully explained in said application, referring to FIG. 1, the friction between the front and rear tires and the surface of the road enables a vehicle to be braked to a stop by braking forces applied to the wheels through the braking system. Hereinafter, where the term stopping force is used, that term refers to the reaction force applied to the tires by the road surface to stop the vehicle, while theterm braking force" refers to the force applied to the wheels to brake the wheels by the wheel brake mechanism. The stopping force S, at the front wheels produced as the vehicle decelerates is equal to the vertical reaction at the front wheels timesthe coefficient of friction F Thus S;= F R Similarly, the stopping force S at the rear wheels equals the product of vertical reaction and the coefficient of friction, so that S, F,R,.

Knowing these relationships and taking a summation of forces and moments about the center of gravity, the Holland equation for 8 /8, can be derived.

Next, in order that this equation may be utilized, the location of the center of gravityis determined for a given vehicle at a given loading, whichmay be accomplished as described in said copending application Ser. No. 708,880.

Having determined the distance dimensions X,.Y and Z of the center of gravity from the wheels and the road surface, a compilation then is made the ratio of the maximum obtainable stopping force at the front wheels to that at the rear wheels for various coefficients of friction between the tires and road, using the equation for S /S,. The coefficients of friction are selected within the range that will be e x perietic ed between the tires and the road during operation of the vehicle. Preferably a curve of this information is plotted as illustrated in FIG. 2.

From the equation for Sf/Srthe following additional relationships may be derived, wherein W is the total weight of the vehicle:

With these latter equations, data may be obtained indicating the maximum stopping force obtainable at the front wheels and at the rear wheels as a function of the coefficient of friction of the tires relative to the road. In so doing, values are taken from the curve of FIG. 2 and inserted into the two formulas for S, and S, noted immediately above. Again, preferably, curves are drawn for the front and rear wheels as indicated in FIG. 3. This represents the ideal condition, i.e. the highest values of stopping forces front and rear that are possible at various coefficients of friction for the vehicle in question.

With this in mind, actual braking force values at various hydraulic pressures in the braking system of a particular vehicle are secured through the use of a dynamometer, by rotating the wheels and measuring the resistance to movement produced by the brakes at different hydraulic pressures. A conventional dynamometer may be used for these measurements. Using these readings of the hydraulic system pressure and braking force, curves preferably are plotted as shown in FIG. 4 illustrating the relationship between hydraulic system pressure and actual braking force for the systems for the front and rear wheels of a given vehicle.

To produce maximum vehicle deceleration, according to the Holland method the actual braking forces produced at the front and rear wheels by the hydraulic brake system of the vehicle (which is graphically shown in FIG. 4) should be controlled by means incorporated in the system so that the relationship of braking force front to rear matches the relationship of stopping force front to rear shown in FIG. 2. Ideally, the actual braking force relationship front to rear should be varied to match the variation in stopping force relationship front to rear shown in FIG. 2. Understanding this aspect is the key to understanding the Holland method.

Putting it another way, when the relationship of braking force front to rear is varied to agree with the required stopping force relationship front to rear illustrated in FIG. 2, maximum vehicle deceleration will be produced under any given tire-road coefficient of friction up to the skid point. With this fact in mind, the next step in the Holland method is to determined how the stopping forces which are required (FIG. 3) can be produced with the given vehicles hydraulic brake system (FIG. 4). This step can be carried out by crossplotting the curves in FIG. 3 and the curves in FIG. 4, which produces the curves of FIG. 5.

Accordingly, the curves of FIG. illustrate the required hydraulic pressures in the front and rear braking systems to produce maximum vehicle deceleration at various tire-road coefficients of friction. In other words, FIG. 5 shows in two curves the relationship between the front hydraulic pressure and the rear hydraulic pressure required to produce the relationship of maximum stopping forces Sf/Sr at any given tire-road coefficient of friction F,. This relationship of front brake line hydraulic pressure to rear brake line hydraulic pressure can be plotted on a single curve using the values on FIG. 5, as shown in FIG. 6, which graph also illustrates the relationship of F, to rear brake line hy draulic pressure.

According to the Holland method of obtaining maximum vehicle deceleration at any given tire-road coefficient of friction, maximum vehicle deceleration will be obtained by matching the braking force relationship front to rear produced by the brake system to the stopping force requirements front to rear established for that particular vehicle by the Holland equation for Sf/Sr. Since-the stopping force ratio S,/S, varies as a non-linear function of coefficient of friction, the braking force ratio varies as a non-linear function of coefficient of friction (as shown in FIG. 6), total braking force, and vehicle deceleration. Furthermore, since the maximum total braking force that can be applied without wheel lock-up is determined by the maximum tireroad coefficient of friction that can be developed at any given road condition between the tires and the road, the ratio of the front to rear braking force to obtain maximum deceleration without skidding will be a function of the maximum tire-road coefficient of friction.

It will also be observed that for any distribution of disposable load in the vehicle, at each coefficient of friction between the tire and the road, there is a single value of braking force that can be applied to the front and a corresponding value of braking force that can be applied to the rear wheels to achieve maximum deceleration of the vehicle without resulting loss of adhesion between the tires and the road. Under dry, paved road conditions (where the value of F, approaches unity) the ratio of front-to-rear braking force is at a maximum. Under other conditions, such as on wet pavement or ice (where the value of F approaches zero), the lower coefficient of friction results in less weighttransfer effect and, consequently, a different distributionof downward tire forces between front and rear, even though the total downward force of the vehicle remains the same. It can, therefore, be seen that the proportioning of braking force between front and rear which is most effective under one condition will not be correct for another condition where a different coefficient of friction is encountered. It is for this reason that conventional hydraulic braking systems with fixed proportioning of braking forces front to rear inherently cannot achieve maximum deceleration. If a braking system is set up to proportion front-to-rear forces to give maximum braking under maximum tire-road friction conditions, with a relatively larger proportion of braking force applied to the front wheels, the use of the same ratio under low friction conditions such as on ice covered pavement will result in an excessive proportion of braking force at the front wheels and consequent underutilization on the rear wheels or impending skidding of the front wheels before the rear wheels are utilized to maximum braking effect. On the other hand, if the fixed proportion is set up to a favor lower friction conditions, then an attemptedmaximum stop under more favorable friction conditions will result in exceeding the adhesion capability of the rear tires by producing a greater proportion of braking force than they can accommodate without skidding. These pressure limiting devices produce a non-continuous front-to-rear brake force relationship. Since the: ratio of frontto-rear braking forces (and consequent hydraulic pressures) required for maximum vehicle deceleration on various types of road friction surfaces does not vary lineraly with the tire coefficient of friction, and is a continu ously This results not only in losing the optimum stopping distance for the vehicle, in the: absence of anti-skid control, it also increases the dangers of losing control of the vehicle because the skidding rear wheels will tend to induce a spin.

In conventional hydraulic brake systems for automotive vehicles, by the simultaneous application of fluid pressure from a master cylinder to individual slave cylinders in the brake mechanisms of each wheel, the brakes are applied concurrently'providing equal or directly proportional braking forces at the front and rear wheels depending upon the relative size of the front and rear slave cylinders. It is also common practice to separate the hydraulic systems between front and rear to assure the operation of one pair of brakes in case the other hydraulic system fails. However, in these split systems, interconnection of the two master cylinders is provided to assure substantially equal front and rear pressures. Occasionally pressure limiting devices and other means have been inserted in the rear brake sys tem to limit maximum rear brake system pressure, or otherwise modify the front to rear braking force relationship in some arbitrary manner. These pressure limiting devices produce a non-continuous front-to-rear brake force relationship. Since the ratio of front-to-rear braking forces (and consequent hydraulic pressures) required for maximum vehicle deceleration on various types of road friction surfaces does not vary linearly with the tire coefficient of friction, and is a continuously varying ratio, as shown in FIG. 6, none of these systems can provide optimum braking effect except at one or two values of coefficient of friction, and must necessarily produce non-optimum results for all other road conditions.

Turning again to FIG. 6, this graph illustrates values of concurrent front and rear hydraulic system pressure at any value of coefficient of friction F for an exemplary vehicle weight, configuration and hydraulic brake system, and which will provide maximum vehicle deceleration. It will be observed that these pressures are not simple straight line relationships, but rather a family of continuous curves of a more complex nature, and are determined for a particular vehicle and not by any arbitrary equalization or non-equalization factor within the braking system for proportioning the braking forces between front and rear.

POWER ACTUATED DEVICES In accordance with this invention, the vehicle braking system is provided with a power actuated variable proportioning device to vary the ratio of braking forces front to rear to match the vehicles requirements for maximum braking, and with a power booster device to assist manual effort in applying the braking forces, both said devices being preferably controlled and operated by a controller consisting of a decelerometer and an augmentor which senses vehicle deceleration and produces a supply pressure for power actuation of both said devices.

VARIABLE RATIO PROPORTIONING DEVICE Turning first to the device for varying the ratio of braking forces front to rear shown schematically in FIG. and in detail in FIG. 11c, this device 48 is adapted for direct mounting to the master cylinder 38 as shown, or it may be mounted on the vehicle and connected with conduits of the conventional type used for vehicle brake lines. As shown herein, the device 48 has a housing 50 having an inlet port 51 for high pressure from the master cylinder rear port 52, and a second inlet port for high pressure from the master cylinder front port 54, with the respective inlet ports being in line with the master cylinder ports so that a conventional coupling or connection (not shown) can communicate the respective ports as well as secure the device 48 to the master cylinder 38.

Because the proportioning device 48 varies the ratio of the front brake line pressure relative to the rear brake line pressure by regulating the rear brake line pressure, the master cylinder front port may communicate through the inlet 53, a drilled passage 55 and an outlet port 56 directly to the front wheel brakes 30 by means of the conduit 34 (FIG. 10) which is suitably connected to the outlet port 56 by a conventional connector (not shown). The device 48 also has a rear outlet port 60 for the rear brake line 61 that is connected to the rear brakes 32.

Variable proportioning is obtained by a regulating valve means 61 which is contained within the housing 50 and regulates the fluid pressure in the outlet port 60 to the rear brake line 61 as a non-linear function of the force produced by an independently operated power actuated means indicated generally at 68, which is operated by an outside source. From the rear high pressure inlet 51, pressure fluid is directed through passages 64 and 65 in the housing 50 into a first cylinder 66 containing a piston 67. The passage 64 also carries high pressure fluid from the inlet 51.into a check valve chamber 70 containing a check valve ball 71 urged by a spring 72 into sealing contact with an opening forming a seat 73 for the ball 71 and leading to a regulated pressure cylinder 74 containing a second piston 75. The regulated pressure cylinder 74 supplies the rear outlet port 60. Both pistons 67 and 75 are provided with seals 77 made of TEFLON or other low friction material, and in the illustrated device, the pistons are constructed'as a single coaxial piston shuttle with the pressure faces of the pistons oppositely disposed and of equal size so that the pressure forces on the shuttle from the high pressure cylinder 66 and the regulated pressure cylinder 75 are in direct opposition. A pin 80 is carried by the second piston 75 which contacts the check valve ball 71.

With the structure thus far described, the valve would operate as a fixed ratio proportioning device utilizing high pressure forces on the first piston 67 which tend to urge the piston shuttle to the right and regulated pressure forces in the pressure cylinder 74 acting on the second piston 75 which tend to urge the second piston and thus the piston shuttle to the left. When the inlet pressure forces on the first piston exceed the regulated pressure forces on the second piston, the piston shuttle will be displaced to the right, moving the ball 71 off its seat 73 and allowing high pressure from the passage 64 to pass through the chambers 70, 74 to the regulated pressure outlet 60. Since as shown the opposing pistons have substantially the same area, in the absence of means to vary the ratio the valve would provide a fixed proportioning ratio of unity between the inlet and outlet pressures. Such a means for varying the ratio is included, herein shown as the independently operated power actuated means 68 which includes a diaphragm assembly 63, and a spring, cam lever arm and connecting means assembly 81 for applying a variable biasing force to the piston shuttle, for varying the proportioning ratio (and the front-to-rear braking force) as a nonlinear function of the varying power or pressure force from an outside source, which applied power or force varies in a known relationship to variations in said inlet 51 pressure, so as to vary the ratio of the regulated outlet pressure to the inlet pressure to match the nonlinear function.

As will hereinafter be described in more detail, the decelerometer portion of the controller included in the braking system and constructed in accordance with the invention produces a pneumatic output or supply pressure when the brakes are applied that is directly proportional to the deceleration of the vehicle. Preferably, the decelerometer portion of the controller is utilized as a source for the proportioning device, since there will be a known relationship between brake line pressure and deceleration. However, the pressure in the power chamber within the power booster included in the braking system is directly proportional to the force being applied to the master cylinder, the brake line pressure, and the braking force applied by the wheel brakes. Alternatively, therefore, the power chamber of the booster may be used as the source of supply fluid pressure to the diaphragm assembly 63.

Whichever source of variable air supply pressure is utilized, it is connected to an inlet port 82 which supplies the pressure to the diaphram assembly 63. The supply pressure is communicated through the passages 83 and 84 to the left sides of two independent diapharagms 85 and 86 which are tandomly connected to a common axial movable shaft 87. The right sides of the diaphragms 85 and 86 are connected through the conduit 90 to a source of vacuum, with the right side of diaphragm 85 communicating through passages 91 and 92 to the right side of diaphragm 86.

The force produced by the diaphragm assembly is transmitted via the assembly 81 which modifies that force according to the shape of the cam lower arm 93 to produce a variable biasing force which acts on the piston shuttle. To this end, the cam lever arm 93 has at one end a hook 94 to which a biasing spring 95 is attached. At the other end, the cam lever arm has a cam surface 96, which is urged by the biasing spring against a connecting means consisting of a lever arm 97 which is pivoted on pin 98 attached to the housing and applies a variable biasing force to the piston shuttle.

' With a vehicle of known size, weight, load distribution and wheel brake mechanism, the biasing spring 95 is selected and the shape of the cam surface 96 on the cam lever arm 93 is determined as described in said copending application Ser. No. 708,880 of Harvison C. Holland so that the contact point of engagement with the lever arm 97 is moved in response to the fluid pressure from the outside source represented by the motion to the piston shuttle. In this way, the ratio of front to rear brake line pressures is varied as necessary to match the specifications therefor as shown for example in FIG. 6 and thereby match the stopping force requirements for both front and rear wheels to achieve maximum deceleration.

The biasing spring 95 is anchored to the housing 50 on a support bar 100 and exerts a force tending to move the cam lever 93 clockwise as seen in FIG. lie. The cam surface 96 of the cam arm is thus urged to the right arid contacts the lever arm 97 at points along its length depending on its position as determined by the motion of the shaft in response to the fluid pressure moving the diaphragms and the shaft 87.

In operation, with a relatively low hydraulic pressure representing relatively small force applied to the brake pedal and small total braking forces resulting in low rates of deceleration, the diaphragm assembly 63, spring 95, cam lever arm 93 and connecting means elements 81 will assume the position shown in solid lines in FIG. 10 with the contact point between the lever arm 97 and the cam lever arm 93 at point A. It can be seen that in this position the mechanical advantage of the biasing spring 95 in acting to move the piston shuttle to the left is small, because the contact point A is toward the tip of the cam lever arm, and near the point of the lever arm. At higher rates of deceleration produced by higher total braking forces, however, the diaphragms 85, 86 will move the shaft 87 to the right, shifting the cam lever arm 93 to some alternate position as indicated in phantom and moving the contact point to B. Here the contact point is in a position which gives the biasing spring 95 a greater mechanical advantage in urging the piston shuttle to the left, increasing the biasing force by an amount greater than the increase in the force of the spring and thus the proportioning of the hydraulic pressures achieved by the device will be corresponding different. As the biasing force on the piston shuttle is increased through the movement of the shaft 87 to the right under increased fluid pressure, the ratio of inlet to outlet pressures will become greater; that is, the outlet pressure to the vehicles rear brakes will be diminished in a non-linear manner as a function of vehicle deceleration.

It is to be noted that for safety considerations, the device is constructed whereby there will be no proportioning and therefore no drain of power to perform proportioning in the event a loss of vacuum occurs. Such a loss would result in a pressure approaching atmospheric pressure on the right sides of the diaphragms 85 and 86 enabling the biasing spring 95 to act on the cam lever arm 93 urging it to the left as shown in position A. In this position the biasing force on the piston shuttle is minimized and the piston 75 having the pin 80 will move the ball 71 off its seat when fluid pressures in the passages 64 and 65 increase to maintain full pressure in the rear brake lines.

The values for the biasing spring 95 and the specific shape of the cam surface 96 are calculated to produce in the operation of the proportioning device the relationship of front wheel hydraulic pressure to rear wheel hydraulic pressure specified for the particular vehicle on which the device is to be installed. For example, the device may be devised to produce the relationship of front to rear wheel hydraulic brake pressures as shown 14 in FIG. 6 for an exemplary automobile and conventional hydraulic brake system. FIG. 7 is a design curve for a proportioning device constructed to obtain the front-to-rear wheel hydraulic pressure relationship illustrated in FIG. 6. Thus a cam surface for the cam lever of the proportioning device is calculated to pro duce pressure in the rear brake lines (P at various inlet pressures from the master cylinder (P,,,,). [t is noted that the cam surface may be changed to compensate for non-linearities within the braking system, for

example, a non-linearity between deceleration of the vehicle and brake line pressure, or a non-linearity between brake line pressure and braking forces. Thus, the cam surface may be calculated to give whatever characteristic is desired between brake line pressure varies braking force, so long as the power source to the power actuated means 68 varies in a known relationship to variations in brake line pressure.

The fluid pressure controlled by the proportioning device will lie within a hysteresis band caused by the delay in opening and closing the check ball valve due to the friction inherent in all moving mechanisms. Based on pressure, spring, and friction force data for the parts of the device, the upper and lower curves are included in FIG. 7 to define the hysteresis band within which the device should operate. The proportioning device also includes a rotatable end cap 101 which is adjustable to adjust the tension on the biasing spring. The rotatable end cap should be in the mid position for the design curve of FIG. 7 which is the middle curve shown in that graph. Rotating the end cap 101 in either one direction or the other raises or lowers the S /S,- curve of FIG. 2 (as illustrated by the dashed curves) to take into consideration vehicle loading, or changes in the brake system or in tire characteristics of the vehicle.

To aid in understanding what is achieved by variable proportioning of brake line pressures in conjunction with control of the total braking force responsive to deceleration, reference is made to FIG. 8 which is a graph of coefficient of friction (F plotted against slip-ratio,

' which is the ratio of the velocity of the tire with respect to the road surface at the point of contact. FIG. 8 is based on test curves published by NASA in report TRR-20 (I959) for aircraft tire-runway performance, and is believed generally representative of automobile tire-road performance. FIG. 8 shows the relationship between coefficient of friction and the amount a tire crawls, slips or slides along the road surface. From FIG. 8 it will be noted that to achieve maximum stopping force at the tire-road surface, a peak value of coefficient of friction must be developed by the application of sufficient braking force to produce the slip-ratio corresponding to that peak value for a given tire and road surface. One objective of variable proportioning as the term is used herein, is to achieve the peak value of coefficient of friction at both front and rear wheels, so as to achieve maximum stopping force at both front and rear wheels. It will also be observed from FIG. 8 that with variable proportioning, applying a total braking force which exceeds that producing the peak value of coefficient of friction will result in an unstable condi tion since an increase in slip-ratio results in a decrease in coefficient of friction which will, in turn, produce more slip and the start of wheel lock-up.

To prevent wheel lock-up and vehicle skidding, the total braking force is reduced at the start of wheel lockup which occurs simultaneously at both front and rear wheels; the total braking force is momentarily held at a lower value to allow the tires to achieve a slip ratio below the peak of the coefficient of friction curve; and then, the total braking force is again increased to achieve the peak coefficient of friction. This cycle is repeated with the result through variable proportioning of modulating the maximum braking forces at both the front and rear wheels about their maximum to maintain maximum deceleration without skidding.

For sensing that wheel lock-up has started, means are included in the system to respond to changes in deceleration of the vehicle. According to the present invention, the deceleration responsive control means takes the form of a pneumatic controller 46 (FIG. 11b), which is operable to control via the booster the total braking force developed with the power assist provided by the booster.

POWER BOOSTER Referring to the schematic illustration of FIG. 10 and detailed in FIG. 11a, the power booster 42 is shown to be of the vacuum suspended type having a casing 122 and a diaphragm supported power wall 124 movably mounted in the casing and connected to the output rod 126 of the device which operates the master cylinder pistons 128, 130. A booster control valve means including a three-way control valve 134 is utilized in the power booster for modulating the pressure in the power chamber 136 behind the power wall 124, while the casing chamber 138 ahead of the power wall is connected through a passage 233 to the vacuum side of the controller 46 (FIG. 11b) and thence to a check valve (not shown) and to the intake manifold 44 of the automobile engine through a hose 140. The three-way control valve 134 is effective to modulate the pressure in the power chamber 136 behind the power wall upon actuation by an actuating rod 142 connected to the brake pedal linkage.

As previously noted, one of the principal features of this invention is control of the total braking force responsive to changes in deceleration of the vehicle reflecting impending wheel lock-up, through control of the power booster. In the form of system shown schematically in FIG. 10, this is achieved by control of the differential pressure across the movable power wall of the booster to modulate the output force produced by the booster and thus the braking forces at both front and rear wheels about that output force required to develop the maximum coefficient of friction between the tire and the road (see FIG. 8) to maintain substantially maximum vehicle deceleration for a given tire-road combination while preventing wheel lock-up and vehicle skidding.

A conventional type of vacuum suspended power booster is supplied with two sources of pressure, vacuum and air"; the present vacuum suspended power booster 42 is constructed to utilize a differential pressure which is modulated by deceleration responsive means over a range, rather than the fixed differential pressure between vacuum obtained from the engine intake manifold and air at atmospheric pressure.

In the present booster, to receive a modulated air pressure from such deceleration responsive means 46 (herein shown as a controller 46) the power wall assembly 124 of the booster 42, as shown in FIG. 11a, is constructed with a sealed air chamber 146 formed between two spaced plates 148, 150, clamped to the inner rim of the supporting diaphragm 152. The air at modulated pressure is conducted to the air chamber 146 through an unrestricted flexible hose 154 carried inside the vacuum chamber 138 of the booster. When sup-' plied from the controller 46, for example, the air is received from the output passage 156 of the controller 46 which is mounted on the vacuum chamber case 122. The air hose 154 is fixed at one end to a tubular elbow 160 welded to and projecting inside the vacuum chamber 138, while the other end of the flexible hose 154 is connected to a fitting 162 on the power wall 124.

Control of the differential pressure across the power wall of the booster in the range of braking forces up to the skid point is achieved by the three-way booster valve 134 which operates over this range in the conventional manner. The pressure in the air chamber 146 on the power wall is maintained at a small differential above the pressure in the power chamber 136 by the decelerometer portion of the controller 46, so that flow of air to the power chamber is provided by actuation of the booster control valve 134 to produce power booster output forces of a magnitude adequate to operate the brakes via the master cylinder actuation. Thus, the valve 134 includes a tubular rubber valve element 164 having a radially extending rubber disc 166 at one end reinforced by a rigid ring 168 and providing concentric air and vacuum valve seats 170, 172. The tubular rubber valve element 164 is supported at its other end, so as to provide for axial movement of the rubber disc, by a flexible skirt 174 which extends radially and is clamped at its outer edge to the power wall 124 in any suitable way. A fixed air valve seat 176 is formed at the inner circular edge of one of the power wall plates 150 and the disc 166 of the valve element is movable onto and off the fixed air valve seat 176 to control flow of air from the air chamber 146 on the power wall 124 to the power chamber 136 behind the power wall.

The vacuum valve of the three-way booster control valve is formed between the vacuum valve seat 172 on the movable disc 166 of the valve element and a cooperating seat 178 formed by the circular forward edge of a valve member 180 operably moved by the brake pedal. This valve member 180 is carried for sliding movement within a tubular rearward extension 182 of the power wall 124, which extension is fastened to the rear plate 150 forming the power wall. The power wall extension 192 slides within a rubber seal 184 on the axis of the booster casing and surrounding the opening in the casing rear wall 186 through which the extension projects. The valve member 180 is operated by the actuating rod 142 connected to the brake pedal linkage, and the valve member 180 extends forward through the open center of the rubber valve element 164 leaving an annular passage around the outside of the valve member which communicates with the vacuum chamber 138 on the forward side of the power wall 124. A power wall return spring 188 is included, and a light spring 190 to positively return the rubber valve element and thereby close the air valve is also included.

The three-way booster control valve 134 is shown in FIG. 11a with the rubber valve element 164 and other components in the fully returned position with the air valve closed and the vacuum valve open; it will be clear that upon application of the brake pedal, the actuating rod 142 will move the valve member 180 forward to engage the vacuum valve seat 172 on the movable rubber valve element thereby closing the vacuum valve in this position of the assembly both the air and the vacuum valves are closed this is commonly referred to as the lapped position of the three-way valve. Further actuation of the brake pedal moves the actuating rod 142 and valve member 180 forward carrying the rubber valve element 164 forward and lifting it off the fixed air valve seat 176, thereby opening the air valve and allowing air in the sealed chamber 146 on the power booster wall 124 to flow into the power chamber 136 behind the power wall. The increase in pressure in the power chamber behind the power wall produces a differential pressure across the power wall which causes the power wall to move forward in the casing, the three-way valve 134 having a self-lapping action which results in the air valve being closed upon forward movement of the power wall and the vacuum valve being maintained closed when the portion of the reaction to the output force developed by the unit transmitted back toward the brake pedal through a reaction mechanism 400 balances the force applied to the brake pedal by the operator. The reaction mechanism 400 may be of conventional construction as illustrated for example, in Bauman US. Pat. No. 3,033,173.

DECELERATION RESPONSIVE CONTROL The controller for controlling the supply pressure to the power booster to control the operation of the booster to prevent wheel lock-up and vehicle skidding, and for controlling the power actuated proportioning device responsive to deceleration to provide maximum braking up to the skid point, will now be described. The controller 46, shown in FIG. 10, schematically and de tailed in FIG. 11b, in general comprises a valve body 210 or housing having a central chamber-defining portion 211. Within the central portion 211 of the valve body there is provided a three-way valve indicated generally at 212, and a dumbell-shaped inertia-mass 213 for actuating the valve 212 to modulate the output pressure from the decelerometer portion of the controller which is the supply pressure to the booster. as a linear function of deceleration, as illustrated graphically in FIG. 9, which supply pressure is conveyed through the passage 156 to the booster 42. The booster is also supplied with vacuum through a vacuum passage 233 via the forward vacuum chamber 229 of the controlling check valve (not shown) and nipple to a vacuum source such as the intake manifold of the engine. Thus, control of the air supply pressure by the decelerometer 46 achieves the desired end of controlling the differential pressure utilized to operate the booster.

Within the central portion 211 of the decelerometer housing 210 are openings for connections to two sources of pressure, a port 215 connecting to atmosphere and a port 216 connecting to line 140 and thence to a source of vacuum. The port 215 is protected by a mesh filter 218 and a perforated screen 219 which serves to filter the atmospheric air as it passes through the port 215.

The inertia-mass 213 is comprised of a shaft member 220 having an enlarged end 221 to which another sepa-' rate inertia member 222 is threadably secured, given the inertia-mass 213 a dumbbell shaped appearance.

The inertia-mass 213 is supported for axial sliding movement in the housing 210. At its forward end (to the left as seen in the drawing) the inertia-mass 213 has a projection 213' of reduced cross-section slidably received in a TFE Teflon bushing 223, and at its rear end the inertia-mass 213 has a recess for a TFE Teflon bushing 225 which receives a protruding stub shaft 226 carried by a diaphragm housing 227 fastened to one end of the valve body 210. Teflon is used as the material for bushings 223, 225 because its coefficient of friction is low and becomes smaller as sliding speed approaches zero rather than larger as is true of other materials. The bushings 223, 225 thus enable freely slidable movement of the inertia-mass 213 in an axial direction within the housing 210 in response to deceleration forces, and inhibit any tendency of inertia-mass 213 to operate in a stickslip manner and thus assist in producing smooth, sensitive operation of spool valve 212.

The chambers defined within the central chamber forming portion 211 of the housing include a first pres sure chamber 228 open to atmospheric pressure through the port 215, a second pressure chamber 229 separated from the first pressure chamber 228 by a wall 230 and connected to the vacuum source through the port 216, and a third output pressure chamber 231 sep arated from the first pressure chamber 228 by a body wall 232. The second pressure chamber 229 is also connected to the vacuum chamber 138 of the power booster 42, through a vacuum passage 233 in the mounting bracket 120. Thus, both the controller vacuum chamber 229 and the booster vacuum chamber 138 are maintained at a sub-atmospheric pressure of about 5 p.s.i.a. by connection to the engine intake manifold 44 through a check valve and a vacuum hose 140 (FIG. 10 and FIG. 12) as compared to the about 14.7 p.s.i.a. available from the atmosphere at the port 215.

The differential between the pressure in the output chamber 231 of the decelerometer portion of the controller and the vacuum source is modulated by controlled opening of an air valve 236 and a vacuum valve 237 which are components of the three-way valve 212. The air and vacuum valves are arranged on a valve spool 238 which is coaxially and slidably received on the intertia-mass 213. Shaft 220 of inertia-mass 213 is sprayed with a light TFE Teflon coating to inhibit stickslip action between inertia-mass 213 and spool valve 212, as described for bushings 223 and 225. The valve spool 238 has internal passages 239 connecting the air and vacuum valves 236, 237 which control or modulate the output pressure in chamber 231 as it relates to the vacuum pressure in chamber 229.

Both the air and vacuum valves 236, 237 comprise annular rings 236', 237' of resilient material inlaid into circular slots in the corresponding faces of the valve spool 238. The inlaid material forms a sealing ring which abuts against a corresponding annular boss 236", 237" which forms a seat. In the case of the vacuum valve 237, the seat 237" thus formed is on the forward-facing surface of section 222 of the inertiamass 213, while the ring 236 of the air valve 236 seats against an annular boss 236" formed in the chamber wall 232 separating the first pressure chamber 228 and the output pressure chamber 231. The arrangement of the components forming the valves 236, 237 has the advantageous feature wherein both valves are operable to close against fluid flow and open with the flow. In other words. the valves are positively closed against fluid flow which tends to urge the valves to open rather than to close. Thus both valves have identical operating characteristics and open and close without stick-slip tendencies due to pressure differential across the valve.

While the valve spool 238 is slidably received on the inertia-mass 213, it is also connected to the body wall 230 by a flexible annular diaphragm 240. The diaphragm 240 is shown having a permanent semicircular set flexed in a rearward direction in response to the atmospheric pressure forces within the first (high) pressure chamber 228. The diaphragm 240 has a mean effective area at a diameter equal to the diameter of the valve rings 236 and 237 so that pressure within the chamber 238 is balanced and does not affect the operation of the valve. In addition, the flow area of valves 236 and 237 is identical so that valve operations on increasing and decreasing pressure differential changes are identical.

The inertia-mass 213 is slidably supported on Teflon bushings 223, 225 in body 210 and is also conencted to the rear portion of body 210 by a flexible annular diaphragm having an effective diameter less than that of diaphragm 240 and valves'236, 237. Passage'244 in body 210 connectsthe output pressure chamber 231 and the cavity 243 aft of diaphragm 245 containing bushing 225 and inertia weight support stub shaft 226. Thus cavity 243 is maintained at the same pressure as chamber 231.

The size and arrangement of valves 236, 237, diaphragms 240, 245, and passage 244 result in the provision of an annulus A of unbalanced pressure area across the inertia-mass 213 between chambers 231 and 229. Thus the force produced by acceleration of the inertia-mass 213 (F=MA) in the direction of the axis of the dumbell is balanced by the pressure difference between chambers 231 and 229 acting on the area A at which time both valves 236 and 237 will be closed (lap position). The use of diaphragm 245 in conjunction with valves 236, 237 and diaphragm 240 permits the selection of a large diameter for valves 236, 237 for high fluid flow capacity with small axial motion while keeping the differential pressure area A to a moderate value thus permitting the use of a moderate sized inertia-mass 213.

A very light (approximately 0.57 lb. initial force in the illustrative embodiment) lap spring 241 is provided between the inertia-mass 213 and the valve spool 238 to urge the valves 236 and 237 toward their closed position and prevent indecisive valve action. This spring creates a slight bias in favor of closing the vacuum valve on reduction of deceleration force and therefore its value must be kept small.

A bias spring 242 is provided between the inertiamass 213 and the diaphragm housing 227. This spring and area A establish the value of the initial pressure differential (Point Z FIG. 9) between the supply chamber 231 and the vacuum chamber 229 at zero deceleration. The slope of the decelerometer characteristic curve Y is determined by the relationship between area A (FIG. 11b) and the weight of the inertia-mass 213. These values and the value of the bias spring are selected to provide a decelerometer characteristic curve Y (FIG. 9) which is parallel to and slightly above the booster characteristic cu-rve X. Curve X describes the performance of the booster as installed in the vehicle. The difference between curve Y and, curve X is the pressure available to cause fluid to flow into the booster when the booster valve is open and is called lead pressure. The lead pressure should be as nearly constant as possible in order that it can be made as small as possible over the operating range of the booster. This can best be accomplished by contouring the booster diaphragm to give it a straight line characteristic in the operating range as shown in FIG. 9. The break at the lower end of the booster characteristic curve where the booster is overcoming brake return springs etc. can be disregarded. The provision of a constant, but small lead pressure serves the purpose of controlling the sudden application of the brakes and thus inhibits spiking. A second purpose will become apparent later under the description of skid control operation.

The use of TFE Teflon for bushings 223, 225 to support the inertia-mass 213 in the body 210 as well as the use of a TFE Teflon coating between the inertia-mass 213 and the spool valve 212 and the use of thin formed impregnated nylon diaphragms 240, 245 reduces friction losses to a negligible amount and permits the narrow hysteresis band for the decelerometer 46 shown in curve Y of FIG.'9. The hysteresis band for the booster 42 is shown in curve X.

In the condition of zero deceleration, the static condition of the unit, air in the air chamber 228 admitted past the air valve seat defined by the resilient ring 236' of the air valve 236, raises the pressure in the output chamber 231 relative to the pressure in the chamber 229. The magnitude of the differential pressure thus created is a function of the force of the bias spring 242 and the size of the resultant area A, when the spool valve 212 is in the lap position. It will be seen that the pressure in the output chamber, which is the supply air for the booster, will increase until the differential pressure acting on the resultant area A produces a force which is substantially equal to the opposing force exerted by the spring 242. This sets the magnitude of the initial differential pressure.

In the dynamic condition, acceleration of the inertiamass 213 produces a force proportional to deceleration (F=ma) which tends to move the inertia-mass 213 forward (to the left in FIG. 1), so as to open the air valve 236 while the vacuum valve 237 is maintained closed, as shown in FIG. 14B. This deceleration produced force is opposed by a pressure produced force, due to the differential in pressure between the low pressure chamber 229 and the modulated pressure chamber 231 acting on the resultant effective area of the annulus A of the inertia-mass 213. The force produced by deceleration of the inertia-mass 213 plus the force of the bias spring 242 acts to move the inertia-mass 213 forward in the valve housing 210 to open the air valve 236 and thereby increase the output or supply pressure from the controller. It is an important feature of the invention that the total movement of the inertia-mass to open the air valve 236 is extremely minute, on the order of thirty to forty thousandths of an inch in either direction from lap position in a physical embodiment of the invention. The air and vacuum valves at their seats have a relatively large diameter (illustratively l.52 inches), and the valves have proportionally large internal passages as shown, however, so as to allow high rates of air flow through the supply passage 156 sufficient even at such small valve openings to operate the power booster 42. Assuming a constant rate of deceleration, air admitted past the valve 236 will increase the supply pressure until the pressure differential between the chamber 231 

1. A deceleration responsive control means comprising a housing having an output port and a pair of inlet ports, and a balanced valve including movable valve elements in said housing, said movable valve elements and housing providing cooperating valve faces and seats providing two flow control means for controlling the pressure in said output port by selective communication with two sources of fluid at differing pressures connected to said inlet ports, one of said valve elements comprising an inertia member movable in response to deceleration forces acting on said inertia member and operably connected to move the other element and operate said flow control means to vary the pressure in said output port as a substantially linear function of deceleration or acceleration forces, a sealing element sealably connected between said housing and said other valve element and having an area substantially equal to one of said flow control means, a sealing element sealably connected between said housing and said inertia member adjacent a dead ended cavity provided between said housing and said inertia member and having an area less than the other said flow control means, and a communicating damping passage between said output port and said cavity, the differential between the output port pressure and the cavity pressure due to flow resistance of said passage providing the balanced valve with a non-linear stiffness characteristic.
 2. A deceleration responsive control means comprising the combination of a three-way valve and means responsive to deceleration for actuating said three-way valve to produce a modulated output pressure by controlling flow selectively from two sources of fluid at differing pressures, said control means including: a housing, a valve spool movably mounted in said housing, a valve element comprising a movable inertia responsive member connected to said valve spool and producing forces proportional to deceleration of said member, said valve spool, housing and member providing cooperating valve faces and seats defining two flow control means, and means responsive to output pressure connected to both said valve spool and said movable member and producing forces counteracting said deceleration forces so that said member moves said valve spool and Controls flow by both said flow control means to produce a modulated output pressure which varies as a substantially linear function of deceleration.
 3. A deceleration responsive control means comprising three-way valve and means responsive to deceleration for actuating said three-way valve to produce a modulated output pressure by controlling flow selectively from two sources of fluid at differing pressures, said control means including: a housing, a valve spool movably mounted in said housing and having aligned, resilient, substantially equal diameter valve rings, said housing presenting an annular valve seat for engagement by one of said valve rings providing a first flow control means, a member movably mounted in said housing connected to said valve spool and producing forces proportional to deceleration of said member and presenting an annular valve seat for engagement by the other of said valve rings providing a second flow control means, a spring between said member and said spool urging said rings into engagement with said seats and resiliently holding both said flow control means in lapped position, a spring between said housing and said member urging said first flow control means toward open position with a predetermined biasing force, both said valve rings and cooperating seats being arranged to close against the flow through said flow control means.
 4. A deceleration responsive control means comprising a three-way valve and means responsive to deceleration for actuating said three-way valve to produce a modulated output pressure by controlling flow selectively from two sources of fluid at differing pressures, said control means including: a housing, a valve spool movably mounted in said housing and having aligned, resilient, substantially equal diameter valve rings, said housing presenting an annular valve seat for engagement by one of said valve rings providing a first flow control means, a member movably mounted in said housing connected to said valve spool and producing forces proportional to deceleration of said member, said member presenting an annular valve seat for engagement by the other of said valve rings providing a second flow control means, a first spring between said member and said spool urging said rings into engagement with said seats and resiliently holding both said flow control means in lapped position, a second spring between said housing and said member urging said first flow control means toward open position with a predetermined biasing force, both said valve rings and cooperating seats being arranged to close against the flow through said flow control means, and means connected to said inertia-mass defining an effective area exposed to the differential between said output pressure and one of said fluid pressures and operable to produce reactive forces opposing said deceleration and first spring forces, said reactive forces bping operable to close said first flow control means when said reactive forces minimally exceed said deceleration and first spring forces, without opening said second flow control means so that said output pressure is varied by said flow control means as a substantially linear function of deceleration, said first spring being effective to resist closing of said first flow control means until said output pressure is at a predetermined value.
 5. A deceleration responsive control means comprising a body defining a low pressure chamber, a high pressure chamber and a modulated output pressure chamber; first and second valve means movably and sealably supported in said body for controlling communication between said chambers, said valve means being operable i. to communicate said output and low pressure chambers while in a first position wherein said first valve means are closed and said second valve means are open, ii. to isolate each of said chambers while in a lapped position, wherein said first and second valve means are Closed, iii. to communicate said output and high pressure chambers while in a second position, wherein said first valve means are open and said second valve means are closed; a first means for resiliently holding siid first and second valve means in said lapped position with a predetermined force; a second means for resiliently holding said first valve means in said open position; an inertia-mass connected to said first and second valve means and producing forces proportional to deceleration of the mass which urge said second valve means toward said second position; and means connected to said inertia-mass defining an effective area exposed to the differential between said output and low pressures and operable to produce reactive forces proportional to said differential acting in opposition to deceleration forces produced by said mass, said reactive forces and said first resilient means opposing and balancing said deceleration forces and said second resilient means at lapped position of said valve means, so that said output pressure is varied by said valve means as a substantially linear function of deceleration.
 6. A deceleration responsive control means comprising a housing having an output port and a pair of inlet ports, and a balanced valve including movable valve elements in said housing for controlling the pressure in said output port by selective communication with two sources of fluid at differing pressures connected to said inlet ports, one of said valve elements comprising an inertia member movable in response to deceleration forces acting on said inertia member and operably connected to move the other element to vary the pressure in said output port as a function of deceleration or acceleration forces, said housing including an independently movable diaphragm assembly adapted to act on said inertia member, a control chamber sealingly separated from the output pressure in the output port by said diaphragm assembly, a feedback passage for connecting a feedback pressure to the control chamber, the feedback pressure originating from an outside source connected to the output chamber, a one-way relief valve in the passage for trapping a higher feedback pressure in the control chamber upon sudden decrease in the feedback pressure, a restricted bypass orifice communicating the feedback passage and the control chamber, the feedback passage and bypass orifice permitting flow in either direction upon gradual change in the feedback pressure, the force produced by the differential between feedback and output pressure across said diaphragm assembly being effective to assist movement of the inertial member in the direction to actuate the valve to further decrease in output pressure, responsive to sudden decrease in deceleration, the trapping of the higher feedback pressure in the control chamber having a regenerative effect due to the action of the diaphragm assembly on the inertia member.
 7. A control means as defined in claim 2 further including a shiftable plunger having a normal position operative to move the inertia member and valve spool to a position opening said first flow control means.
 8. A control means according to claim 7 further including means for shifting said plunger from said normal position to allow said inertia member to operate responsive to deceleration forces in a given direction.
 9. A deceleration responsive control means comprising a housing having an output port and a pair of inlet ports, and a balanced valve including movable valve elements in said housing for controlling the pressure in said output port by selective communication with two sources of fluid at differing pressures connected to said inlet ports, one of said valve elements comprising an inertia member movable in response to deceleration forces acting on said inertia member and operably connected to move the other element to vary the pressure in said output port as a function of deceleration or acceleration forces, and an On-Off assembly adapted to move saiD inertia member responsive to an external signal to a position wherein said valve communicates the higher pressure source with said output port, notwithstanding the action of deceleration forces in any direction on said inertia member.
 10. A control means as defined in claim 9 in which said assembly includes first and second On-Off chambers, and movably mounted On-Off diaphragm assembly sealingly separating said chambers, said first and second On-Off chambers being adapted to be supplied with external pressures providing a differential pressure across the diaphragm assembly creating a force for moving said inertial member to a position wherein said valve communicates the higher pressure source with said output port, notwithstanding the action of deceleration forces in any direction on said inertia member.
 11. In a skid controller for use with a power brake system on a wheeled vehicle having a manually operated means for controlling a power unit for varying the hydraulic pressure in the system to operate the brakes, a first means responsive to the deceleration of the vehicle for supplying a predetermined minimum positive fluid pressure differential gradient to the power unit whereby application and release of said manually operated means applies and releases the power unit during deceleration within the deceleration ability of the vehicle brake system, a second means for increasing the speed of response and duration of the release action of said first means responsive to a sudden lowering of the deceleration ability of the vehicle and brake system reflecting impending wheel slip toward lock-up, said second means supplying a negative fluid pressure differential to the power unit to reduce the power from said power unit applying the brakes of the vehicle at any level of brake application notwithstanding the continued application of said manually operated means. 